domains

list=symbol*

predicates

more(symbol, symbol)
less(symbol, symbol)
iscity(symbol)
iscmd(symbol)
solve(symbol,symbol,symbol,symbol,symbol,symbol)

solvel(list, list, integer)
iscityl(list, integer)
iscmdl(list, integer)
lessl(list, list)
notmorel(list, list)

goal

/**
 * GOALS. Uncomment your chose.
 */

%solve(A,B,C,X,Y,Z).
%solvel(L1, L2, 3).

clauses

/**
 * CHAPTER 0: Data
 */

% List of known references
more(krasnodar, chelyabinsk).
more(samara, chelyabinsk).
more(dinamo, krasnodar).
more(spartak, torpedo).

% List of known cities
iscity(krasnodar).
iscity(chelyabinsk).
iscity(samara).

% List of known teams' names
iscmd(torpedo).
iscmd(spartak).
iscmd(dinamo).

/**
 * CHAPTER 1: Predicates for fixed data.
 */
less(A, B):-A<>B,not(more(A, B)).

solve(A,B,C,X,Y,Z):-
iscity(A),iscity(B),iscity(C),
iscmd(X),iscmd(Y),iscmd(Z),
not(more(X, A)),
not(more(X, B)),
not(more(X, C)),
not(more(Y, B)),
not(more(Y, C)),
not(more(Z, C)),

not(more(A, X)),
not(more(A, Y)),
not(more(A, Z)),
not(more(B, Y)),
not(more(B, Z)),
not(more(C, Z)),

less(A, B),
less(A, C),
less(B, C),
less(X, Y),
less(X, Z),
less(Y, Z).

/**
 * CHAPTER 2: Predicates for array data.
 */
iscityl([], 0) :- !.
iscityl([H|T], N) :- Ndec=N-1,iscity(H), iscityl(T, Ndec).

iscmdl([], 0) :- !.
iscmdl([H|T], N) :- Ndec=N-1,iscmd(H), iscmdl(T, Ndec).

notmorel(_, []).
notmorel([H1|T1], [H2|T2]) :- not(more(H1, H2)), notmorel(T1, T2), notmorel([H1|T1], T2).

lessl(_, []).
lessl([H|T], [H|T]) :- lessl([H|T], T).
lessl([H1|T1], [H2|T2]) :- less(H1, H2),lessl(T1, T2),lessl([H1|T1], T2).

solvel(LCity, LCmd, N):-
iscityl(LCity, N), iscmdl(LCmd, N),
notmorel(LCity, LCmd),
notmorel(LCmd, LCity),
lessl(LCmd, LCmd),
lessl(LCity, LCity).